Garralepis sp.
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publication ID |
https://doi.org/ 10.5252/g2013n3a3 |
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persistent identifier |
https://treatment.plazi.org/id/493F87AA-FF8D-623E-697D-FC9AFD99FBF8 |
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treatment provided by |
Marcus |
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scientific name |
Garralepis sp. |
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( Fig. 9A, B View FIG )
MATERIAL. — Specimen GIT 580-21: scale.
LOCALITY AND STRATIGRAPHIC HORIZON. — Locality (sample) 73, Tonnel’nyj Brook, south of De Long Strait , Chukotka ; Lower Member (1) of Enmakaj Formation, Lochkovian .
DESCRIPTION ħe one scale GIT 580-21 has a kite-shaped crown 0.9 mm long with smooth straight lateral edges that converge at c. 60°, and three short ridges running back from the rounded anterior crown edge ( Fig. 9A, B View FIG ). ħe central area of the crown is eroded, but the sides are well preserved and slightly higher than the central area. ħe scale neck is very short anteriorly and slightly deeper laterally; the base is strongly convex, and deepest below the level of the anterior crown. Closely spaced grooves encircling the base mark the insertion of Sharpey’s fibre layers.
COMPARISON Although larger than the type scales from the Garra Formation (Lochkovian) of central New South Wales, Australia, the scale matches their simple morphology ( Burrow2002:figs16E-G,30A-H).ħe well-preserved lateral crown edges indicate this region is composed of orthodentine rather than mesodentine or enameloid; both latter tissue types are strongly eroded in the Chukotka microremains. Scales of Nostovicina lacrima (Valiukevičius, 1994) (Valiukevičius 1994) from the Lochkovian ofTaimyr andTiman-Pechora, northern Russia, and more recently identified from coeval deposits in central New South Wales ( Burrow 2002) have a similar shape, but have a mesodentine crown, whereas scales of Garralepis simplex Burrow, 2002 are characterized by having orthodentine crowns with enameloid in upper central layers of the growth zones. ħe simple but characteristic morphology, associated with non-mesodentinous histology, have not been identified in scales of any other known taxa; however, as the identification is based on a single scale, it is only tentatively assigned to Garralepis .
ISCHNACANTHIFORMES ? indet. ( Fig. 9C View FIG )
MATERIAL. — Specimen GIT 580-26: tooth with broken base.
LOCALITY AND STRATIGRAPHIC HORIZON. — Locality (sample) 73, Tonnel’nyj Brook, south of De Long Strait , Chukotka ; Lower Member (1) of Enmakaj Formation, Lochkovian .
DESCRIPTION ħe tooth is c. 2.5 mm high, subtriangular in cross-section with at least one sharp vertical carina, and multiple canals visible in the broken base ( Fig. 9C View FIG ). Surficial tissue along the visible carina is well preserved compared with the rest of the tooth, indicating it is probably orthodentine while the rest of the tooth is probably mesodentine. ħe tooth appears to be flattened, presumably labio-lingually.
COMPARISON ħe cross-sectional shape of the tooth resembles that of the main cusps on dentigerous jaw bones and tooth whorls of ischnacanthiform acanthodians, e.g., the poracanthodid Zemlyacanthus menneri (Valiukevicius, 1992) (Valiukevičius 1992: pl. 4.2; 8.1, 3) from the Lochkovian of Severnaya Zemlya. ħe relatively large size of the tooth is consistent with the size range of these structures also, rather than the much smaller palatine teeth that are also found in ischnacanthiforms (e.g., Valiukevičius 1992: fig.4C). Both tooth whorls and dentigerous jaw bone cusps of Z. menneri show a dense reticulated network of canals in the tooth bases (e.g., Valiukevičius 1992: fig. 8), and tissue differentiation between the tooth carinae (orthodentine) and the rest of the tooth (osteodentine), characters that are also seen in GIT 580-26. None of the acanthodian scale taxa in the Chukotka assemblage have been associated with dentigerous jaw bones or tooth whorls at other localities. ħe tooth is tentatively assigned to the Ischnacanthiformes , as it could possibly be from other acanthodians with tooth whorls having pointed main cusps (see Burrow & Turner 2010).
Incertae ordinis et incertae familiae Genus Nostovicina
Valiukevičius & Burrow, 2005
Nostovicina guangxiensis (Wang, 1992) ( Fig. 9 View FIG D-F)
MATERIAL. — ħree specimens GIT 580-14, 580-15 and 580-18: scales.
LOCALITY AND STRATIGRAPHIC HORIZON. — Locality (sample) 73, Tonnel’nyj Brook, south of De Long Strait , Chukotka ; Lower Member (1) of Enmakaj Formation, Lochkovian .
DESCRIPTION ħree scales conform to the three commonest morphotypes of Nostovicina guangxiensis , with all having equal width and length, a flat rhombic crown that is smaller than the base, and variably developed lateral crown edges ( Fig. 9 View FIG D-F). Scale GIT580-18 ( Fig. 9D View FIG ) exemplifies the most common form of N. guangxiensis , with strong ridges extending back from the anterior edge, and short oblique ridges running down from the posterior corner of the crown; the scale is c. 1.3 mm long and wide. ħe crown on GIT 580-14 ( Fig. 9E View FIG ) is 0.7 mm long, heavily eroded and cracked, with scalloped anterior edges indicating the scale originally had four or five crown ridges. ħe lateral ledges join to form a posterior point extending slightly beyond the posterior corner of the base. Scale GIT 580-15 ( Fig. 9F View FIG ) is c. 1.4 mm long and wide, and is also very poorly preserved with worn remnants of one lateral ledge, a rounded anterior crown margin, and three ridges extending about a third the length of the crown.
COMPARISON ħe lack of histological information hampers identification of the scales, with their shapes fitting within the broad range exhibited by those of Nostolepis striata Pander, 1856 . Another taxon Nostovicina laticristata Valiukevičius, 1994 (Valiukevičius 1994) from various Lochkovian circum-Arctic localities in northern Canada and Russia has similar morphotypes, but its scales are very small with a deep rounded base. Type scales of Nostovicina guangxiensis are from the Early Devonian of Guangxi, China (Wang 1992); the taxon is one of the commonest acanthodians in microvertebrate assemblages from Lochkovianearly Pragian deposits throughout southeastern Australia ( Burrow 2002). ħe older teleostome Yealepis douglasi Burrow & Young, 1999 from the Ludlow of Victoria, Australia ( Burrow & Young 1999), has scales with identical morphotypes and comparable size to the Early Devonian ones, but their histology is unknown. Scales with the same shape and histology as N.guangxiensis are also found in Silurian-Devonian boundary beds of the Birch Creek Section BCII, Roberts Mountains, Nevada, USA and the Klonk section, Czech Republic (Burrow et al. 2010).
Incerti ordinis
Incertae familiae Genus Cheiracanthoides Wells, 1944
Cheiracanthoides rarus Valiukevičius, 1994 ( Fig. 9G, H View FIG )
MATERIAL. — Specimen GIT 580-20: scale.
LOCALITY AND STRATIGRAPHIC HORIZON. — Locality (sample) 73, Tonnel’nyj Brook, south of De Long Strait , Chukotka ; Lower Member (1) of Enmakaj Formation, Lochkovian .
DESCRIPTION ħe one scale GIT 580-20 is 1.0 mm wide, 1.0 mm long; the crown and base have a square outline ( Fig.9G, H View FIG ). ħe crown surface is almost flat, curving down slightly along the anterior edges. Multiple short closely-spaced ridges probably ornamented these edges, although only those towards the centre of the scale are preserved with the rest of the crown being heavily eroded ( Fig. 9G View FIG ). ħe neck is concave and a constant depth of c. 0.15 mm all round. ħe base is convex, with a maximum depth of 0.4 mm. No pores are visible on the scale neck ( Fig. 9H View FIG ).
COMPARISON ħe scale features are very poorly preserved, but the general shape and proportions match those of scales of Cheiracanthoides rarus from the Lochkovian of Taimyr, northern Russia.
Class SARCOPTERYGII Romer, 1955 Clade RHIPIDISTIA Cope, 1887 Clade DIPNOMORPHA Ahlberg, 1991 †Order POROLEPIFORMES Jarvik, 1942 Family POROLEPIDIDAE Berg, 1940 Genus Porolepis Woodward, 1891
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Institute of Geology at Tallinn University of Technology |
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.